1. Field
The present disclosure relates generally to spacecraft and, in particular, to coupling systems for spacecraft. Still more particularly, the present disclosure relates to a method and apparatus for a spacecraft docking system.
2. Background
Spacecraft coupling systems provide a way to mechanically connect two or more spacecraft to each other. A spacecraft, as used herein, is a vehicle, vessel, or machine configured to perform a number of operations in space. Spacecraft may be self-propelled space vehicles configured for short-term space missions, or spacecraft that are configured to remain in space for a longer period of time. In other cases, a spacecraft may be a space station, a satellite, or some other suitable structure.
Coupling two spacecraft may be desirable to transfer resources from one spacecraft to another spacecraft. For example, a space shuttle may dock at a space station to provide crew and supplies for the space station. In other examples, a space shuttle may dock with a satellite to perform maintenance and rework one or more of the components of the satellite.
In this illustrative example, the pair of spacecraft to be coupled includes an active vehicle and a target structure. The active vehicle is the spacecraft that is approaching the target structure. For instance, the active vehicle may be a spacecraft, while the target structure is a space station. The spacecraft approaches the space station for coupling. The coupling of two spacecraft may be referred to as docking or berthing.
With docking, the active vehicle maneuvers under its own propulsion to bring the two halves of the coupling system, one on the active vehicle, and one on the target structure, within the required vicinity of each other. With that requirement satisfied, the docking system is then used to couple the spacecraft together. The docking system is designed to tolerate initial misalignments between vehicles with the docking system providing the ability to still capture, align, and rigidly connect the active vehicle and target structure. In some cases, the active vehicle slows or stops its movement toward the target structure and extends the docking system outward to meet and align with the target structure.
Berthing, on the other hand, occurs when an externally attached device associated with one of the spacecraft is used to bring the active vehicle to within the required vicinity of the target structure. In some cases, this device is a robotic arm that attaches one spacecraft to the other spacecraft and guides the structures toward one another in preparation for coupling.
With the use of coupling systems for spacecraft, controllers are designed to articulate the coupling system in order for the active half of the coupling system to successfully capture the target structure, align the two, and prepare the two halves for establishment of a rigid connection. These controllers for spacecraft coupling systems, however, may be more complex than desired. For example, complex control laws may be needed to ensure that the active vehicle and the target structure engage in a desired manner. These systems also may be heavier than desired for the spacecraft.
Moreover, as the complexity of the control systems for coupling spacecraft increases, the possibility of failure of the coupling system increases due to the more numerous failure possibilities at the subsystem and component level. Therefore, it would be desirable to have a method and apparatus that take into account at least some of the issues discussed above, as well as other possible issues.